Pre-operative 3-DCRT vs IMRT for Locally Advanced Rectal Cancer

Inclusion Criteria: * Patients undergoing pre-operative pelvic chemo-radiotherapy for histologically confirmed rectal adenocarcinoma, with the following staging: cT3N0-2, cT4N0-2, cT(any)N1-2, cT(any)N(any) CRM at-risk \[AJCC version V\] * Staging / imaging of pelvis with MRI, and CT Thorax/Abdomen * No evidence of metastatic disease * ECOG Performance Status 0 - 2 * Age \> or equal to 18 years * Provision of written informed consent in line with ICH-GCP guidelines Exclusion Criteria: * Previous radiotherapy to the pelvic region * Patients in whom induction chemotherapy has been delivered prior to chemo- radiotherapy * History of inflammatory bowel disease * Previous hip replacement * Previous bowel surgery (excluding procedures/operations which would not result in small bowel adhesions - at the discretion of the Principal Investigator) * Patients with other syndromes/conditions associated with increased radiosensitivity * Any other co-existing malignancies within the past 5 years other than non- melanoma skin cancer * Pregnancy or lactation at the time of proposed randomisation * Evidence of any other significant clinical disorder or laboratory finding that makes it undesirable for the patient to participate in the study or if it is felt by the research / medical team that the patient may not be able to comply with the protocol